The IEEE 802.x specifications are a group of network standards defined by ISO.
IEEE 802.12 deals with the low level - Data Link Layer.

The Data Link Layer is divided into two sublayers:

Logical Link Control (LLC).
This sublayer establishes the transmission paths between computers on a network.

Media Access Control (MAC). On a network, the network interface card (NIC) has an unique
hardware address which identifies a computer or peripheral device. The hardware address is
utilized for the MAC sublayer addressing.

The IEEE 802.12 100 VG - AnyLAN is a high-speed network with a data rate of 100
megabits per second (Mb/s) which can be transmitted over several types of twisted pair
cable including single or multiple mode fiber optic cable.
The 100VG-AnyLAN data packets can be encapsulated by IEEE 802.5 Token Ring or IEEE 802.3 Ethernet frames. The packets
can also be routed across FDDI, ATM, and wide area networks. For media access, a packet is
formatted with a training frame that is initially utilized by the IEEE 802.12 interface.
This initialization determines whether the packet is normal or high priority (for example,
multimedia video or audio data) according to the Demand Priority Access Method media protocol (DPAM).

IEEE 802.12 Frame:

Start Frame

IEEE 802.12 packet

FCS

Start Frame.
Indicates that the frame is about to begin.

IEEE 802.12 Packet Training Frame format.

00

01

02

03

04

05

06

07

08

09

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Destination Address

Destination Address

Source Address

Source Address

Requested Configuration

Allowed Configuration

Data :::

Destination Address.
6 bytes.
Contains a null destination address.

Source Address.
6 bytes.
To pass training, an end node must use its source address in the source address field of the training frame.
A repeater may use a non-null source address if it has one, or it may use a null source address.

Requested Configuration.
16 bits.
The requested configuration field allows the slave mode device to inform the master mode
device about itself and to request configuration options. The training response
frame from the master mode device contains the slave mode device's requested configuration
from the training request frame. The currently defined format of the requested
configuration field as defined in the IEEE Standard 802.12-1995 standard is shown below.
Please refer to the most current version of the IEEE document for a more up to date description of this field.
In particular, the reserved bits may be used in later versions of the standard.

First Byte

Second Byte

7

6

5

4

3

2

1

0

7

6

5

4

3

2

1

0

v

v

v

r

r

r

r

r

r

r

r

F

F

P

P

R

Description

vvv:

The version of the 802.12 training protocol with which the training initiator is
compliant. The current version is 100. Note that because of the different bit
ordering used in IEEE and IETF documents this value corresponds to version 1.

r:

Reserved bits (set to zero)

FF:

00 = frameType88023.

01 = frameType88025.

10 = reserved.

11 = frameTypeEither.

PP:

00 = singleAddressMode.

01 = promiscuousMode.

10 = reserved.

11 = reserved.

R:

0 = training initiator is an end node.

1 = the training initiator is a repeater.

Allowed Configuration.
16 bits.
The allowed configuration field allows the master mode device to respond with the allowed configuration.
The slave mode device sets the contents of this field to all zero bits.
The master mode device sets the allowed configuration field as follows:

First Byte

Second Byte

7

6

5

4

3

2

1

0

7

6

5

4

3

2

1

0

v

v

v

D

C

N

r

r

r

r

r

F

F

P

P

R

Description

vvv:

The version of the 802.12 training protocol with which the training responder is
compliant. The current version is 100. Note that because of the different bit
ordering used in IEEE and IETF documents this value corresponds to version 1.

D:

0 = No duplicate address has been detected.

1 = Duplicate address has been detected.

C:

0 = The requested configuration is compatible with the network.

1 = The requested configuration is not compatible with the network and/or the
attached port. In this case, the FF, PP, and R bits indicate a configuration that
would be allowed.

DPAM, Demand Priority Access Method.
(RFC 2266, page 8)
An IEEE 802.12 repeater can be configured to operate in either Ethernet or Token Ring
framing mode. This only affects the frame format and address bit order of the frames on
the wire. An 802.12 network does not use the media access protocol for either Ethernet or
Token Ring. Instead, IEEE 802.12 defines its own media access protocol, the Demand
Priority Access Method (DPAM). There is an existing standards-track MIB module for
instrumenting IEEE 802.3 repeaters [RFC 2108]. That MIB module is designed to instrument
the operation of the repeater in a network implementing the 802.3 media access protocol.
Therefore, much of that MIB does not apply to 802.12 repeaters. However, the 802.3
Repeater MIB also contains a collection of objects that may be used to map the topology of
a network. These objects are contained in a separable OBJECT-GROUP, are not
802.3-specific, and are considered useful for 802.12 repeaters. In addition, the layer
management clause of the IEEE 802.12 specification includes similar functionality.
Therefore, vendors of agents for 802.12 repeaters are encouraged to implement the
snmpRptrGrpRptrAddrSearch OBJECT-GROUP defined in the 802.3 Repeater MIB.

Master Mode Operation.
(RFC 2020, page 9, RFC 2266, page 4)
In an IEEE 802.12 network, "master" devices act as network controllers to decide
when to grant requesting end-nodes permission to transmit. These master devices may be
repeaters, or other active controller devices such as switches. Devices which do not act
as network controllers, such as end-nodes or passive switches, are considered to be
operating in "slave" mode.

Training Frame.
(RFC 2020, page 10, RFC 2266, page 4)
Training frames are special MAC frames that are used only during link initialization.
Training frames are initially constructed by the device at the lower end of a link, which
is the slave mode device for the link...Training frames are always sent with a null
destination address.
To pass training, an end node must use its source address in the source address field of the training frame.
A repeater may use a non-null source address if it has one, or it may use a null source address.